Earlier this week, engineers on the site installed a full circle of giant concrete rings that form the runnel about 32ft (10m) under the east of Pollok Park at a point that is 1.55 miles (2.5km) along the route. More than 1,600 of these concrete rings have been completed so far.

Since the project began, over 150,000 tonnes of earth, stone, clay and other aggregates has been shifted, with site workers having put in more than one million man hours.

The complete section of the tunnel is already capable of holding the equivalent of 18 Olympic-sized swimming pools.

Expressing his joy that the project had reached its halfway point, Scottish Water’s capital investment general manager, Paul Kerr said: “We are delighted to have reached this milestone half-way stage in the tunnel construction.

“The Shieldhall Tunnel team includes some of the best and most experienced tunnellers in the world and they are making great progress with what is the biggest project of its type Scottish Water has ever undertaken.”